1. Field of the Invention
The present invention relates to an automotive headup display apparatus in which an image of the display is reflected by a reflecting surface on the windshield toward a driver's seat so that the display image can be seen within a driver's viewing field on the windshield.
2. Prior Art
An apparatus of this kind which is commonly available is shown in FIG. 8. In this apparatus, display light from an indicator unit 12 installed in the dashboard 11 is reflected by the windshield 13 toward a driver's seat so that a virtual image 15 of the display, when seen from the viewing point 14, can be seen within a driver's viewing field on the windshield 13. The driver therefore can look at the display such as vehicle speed without having to turn away his or her eyes from the viewing field on the windshield 13 while driving.
As shown in FIG. 9, the indicator unit 12 contains an indicator 121 and a reflecting mirror 122. In an opening directed toward the windshield 13, it also has a Fresnel lens 123 mounted in such a manner that the display surface 121a of the indicator 121 lies within a focal point of the lens. The reflecting mirror 122 for reflecting the light coming from the display surface is used to elongate the light path while reducing the size of the unit. The Fresnel lens 123 enlarges the image of the display so that the virtual image can be seen at a position farther than the indicator 121. That is, as shown in FIG. 8, the virtual image 15 is formed in front of the windshield 13 with respect to the forward driving direction, making it easy for a driver to quickly focus on the virtual image.
This kind of apparatus, however, has drawbacks. Since the apparatus utilizes the upper surface of the dashboard, external light as from the sun may enter the indicator, with the result that the display is easily obscured or washed out and the indicator is susceptible to deterioration. Particularly when sun rays directly enter the Fresnel lens 123, they are mostly converged on the display surface 121a of the indicator 121, significantly exacerbating the wash-out phenomena and the deterioration of the indicator.